Gigs - Sitting is preferable but if the stalls are standing I will stand.
Football - Standing. I like it just before kick off when most people are sitting but you see the odd man still standing, arms folded, like an arctic sea bird.
Public transport - 100% sitting

I'm massive, so if it's anything like football or music I'm considerate and try not to get in everyone else's way. I tend to stand up to gesticulate and shout obscenities at Stewart Downing quite a bit at football though, but for the majority of the match I'm seated.

Pubs - standing. it's more social.
Gigs - standing. it's more involving.
Sports - sitting. i had to stand for 4 hours at a college football game in the states and the next day i couldn't walk (i'd stop from 10am at the tailgating until kick off and then at the bar until 2am).
Public transport - depends. a short trip is standing, a long trip is sitting. definition: > 30 mins is a long journey.

Football - Standing if the option's there, i.e. away games. It seems to encourage singing/ a better atmosphere. Most home crowds I've vissited are almost totally silent. People bang on about St James' being loud, but that only happens at big games now; it's usually like a morgue, which feels horrible

I worry that I'll just make myself sleepier. I do like a nice sitting interval though, now and again. My favourite thing to do though is to perch rather than sit. On a bar stool, or edge of chair/ knee of friend.

Pubs - Sitting, I don't like standing when I'm conversing very much... also I find it hard to talk to the shorter people, especially if the is music playing loudly or a lot of people speaking at once... sitting fixes this dilemma most of the time.

Gig - Standing, I just find something very difficult about actually enjoying a gig whilst having a sit.. well obviously this depends on the venue and type of music on display but 9 times out of 10 I'd find myself stood in the middle of the crowd because the atmosphere is there and the sound is often way better, plus you can do more then tap your foot along if you feel like it.